In the double-slit experiment, when conducting it with single particles or single photons, it is indeed important to ensure that only one particle is fired at a time. Achieving this level of control can be challenging, but there are techniques that can be employed to approximate the firing of single particles.
One common approach is to use a device called a "particle source" that produces particles or photons one at a time. This can be achieved by using a low-intensity source, such as a single-photon source or a source that emits particles at a very low rate. By carefully adjusting the experimental setup, it is possible to isolate individual particles or photons to be sent through the double-slit apparatus.
Regarding the walls of the slits, they are typically made of a material that allows for the passage of particles or photons. In the case of photons, the slits can be made by blocking a portion of a light beam, using materials such as metal or cardboard with small openings. For particles like electrons, the slits can be made by using thin material, such as metal foils, with small apertures.
It's worth noting that the specific materials used for the slit walls can depend on the nature of the experiment, the type of particles or photons being used, and the desired properties of the setup (e.g., blocking unwanted particles, minimizing interference effects). The choice of material is typically based on factors such as its transparency to the particles or photons being studied, its structural properties, and its compatibility with the experimental conditions.
Overall, the experimental setup for the double-slit experiment with single particles or photons requires careful control and precise techniques to ensure the firing of particles one at a time and the construction of the slits using appropriate materials.